The exceptionally high-strength and modulus of ultrahigh molecular weight polyethylene (UHMW-PE) fibers and their relatively low density compared with carbon, polyaramide, and metallic fibers has led to their preferred use in a number of high performance textile constructs and industrial, fiber-reinforced composites of thermoplastic and thermosetting polymers. Among the key reasons for their growing use in fiber-reinforced composites is the fact that the UHMW-PE density is about 1 g/cm3; thus, a small weight fraction of the UHMW-PE fibers in these composites provide relatively high volume fractions. Meanwhile, the successful use of UHMW-PE in high-strength textile fabrics and high performance composite applications drew the attention of contemporary medical and bioengineering investigators and inventors. Subsequently, an increasing percentage of the prior art dealing with the use of UHMW-PE fibers pertained to biomedical applications, such as their use (1) in self-reinforced composites, where less than 10 weight percent of fibers resulted in significant increases in the UHMW-PE matrix (U.S. Pat. No. 5,834,113); (2) after chemically activating the surface to increase the adhesion of the UHMW-PE fibers to reinforced traditional matrices of medical significance, such as polymethyl methacrylate and epoxy resins (U.S. Pat. No. 6,069,192); and (3) in combination with other synthetic fibers, namely the non-absorbable polyethylene terephthalate (PET) or the absorbable poly-p-dioxanone (PDS) fibers as orthopedic sutures and allied ligating devices (U.S. Pat. Nos. 7,077,863; 7,066,956; 7,029,490; 6,716,234; 6,652,563). However, investigators who used UHMW-PE fibers or their blends with PET or PDS fibers as orthopedic sutures, ignored a less obvious disadvantage of UHMW-PE that is associated with its exceptionally high modulus, namely, the poor biomechanical compatibility with the cellular components of most biological tissues. And simple blending of UHMW-PE fibers with the high glass transition temperature (Tg) PET fibers, does not mediate the overall stiffness and temper of the poor biomechanical compatibility of suture constructs made thereof. Furthermore, using high compliance PDS fibers in a blend with UHMW-PE to form orthopedic sutures with a staged strength retention profile and partial mass loss to encourage early tissue ingrowth to stabilize the remaining long-term UHMW-PE component of the implant can result in a new clinical problem. The latter can be associated with an early loss of PDS strength leading to a premature decrease in the load-bearing capacity of the UHMW-PE-based orthopedic device prior to the conclusion of the critical period for significant bone regeneration, particularly in patients with compromised tissue healing. This prompted the pursuit of the study of a group of fiber-reinforced composites comprising compliant polyaxial copolyesters and at least one biostable reinforcing yarn made of UMWPE polypropylene and a polyalkylene terephthalate, subject of this invention. Of special interest among these composites are the ones based on UMWM-PE yarn, which provide (1) a solution for mediating the effect of UHMW-PE stiffness on living cells through encasing the UHMW-PE-based fiber blends in a highly compliant, absorbable matrix, which presents these cells with a biomechanically compatible surface; (2) substituting the non-absorbable, high Tg PET with a low Tg segmented absorbable copolyester, which does not only impart a higher biomechanical compatibility to the UHMW-PE fiber-based construct, but also allows more timely and prolonged mass loss and strength loss profiles compared to PDS fiber; and (3) natural, highly biocompatible silk fibers as a component of the reinforcing fibrous construct to support natural tissue regrowth and engineering—silk fibers have been described as a useful matrix for tissue engineered anterior cruciate ligaments [Altman, G. H. et al., Biomaterials, 23(20), 4131 (2002)].
As discussed above, the concept of combining absorbable and non-absorbable fibers has been applied, to a limited extent, to produce partially absorbable hernial meshes and vascular devices. In addition, the present inventors have described in a recent disclosure, totally absorbable/biodegradable composites comprising at least two fibrous components with distinctly different individual physicochemical and biological properties for use in constructing absorbable/biodegradable medical devices or surgical implants, such as meshes and vascular grafts displaying a gradient in clinically relevant properties (U.S. patent applications Ser. Nos. 11/886,370 and 11/879,357 filed on Sep. 14, 2007 and Jul. 17, 2007, respectively, each of which are hereby incorporated herein by reference in their entireties). However, none of the early prior art and recent disclosures dealt with selectively absorbable/biodegradable, composite constructs comprising combinations of biodegradable and biostable yarns assembled as initially interdependent, load-bearing components transitioning to exhibit independent functional properties during in vivo end-use in degrading environments. And this, in part, prompted the pursuit of a second group of selectively absorbable, specially warp-knitted, composite fibrous constructs with or without an absorbable surface coating.